Although it has long been possible to make organic materials emit light, it has only recently become possible to do so at the level and with the efficiency and control necessary to make the materials a useful basis for illumination or displays. The early electroluminescent devices provided reasonably bright light, but required high operating voltages, produced only a narrow range of colors, and had severely limited lifetimes. Recent developments, however, make it possible to manufacture organic light-emitting devices that are thin, bright, efficient, and stable and that produce a broad range of colors. This book surveys the current status of the field. It begins with an overview of the physics and chemistry of organic light emitting devices by J. Shinar and V. Savvateev. Subsequenbt chapters discuss the design of molecular materials for high performance devices (C. Adachi and T. Tsutsui) and chemical degradation and physical aging (K. Higginson, D. L. Thomsen, B. Yang, and F. Papadimitrakopoulos). A. Dodabalapur describes microcavity OLEDs, and Y. Shi, J. Liu, and Y. Yang discuss polymer morphology and device performance. Various aspects of devices based on polyparaphenylene vinylenes are discussed in chapters by N.C. Greenham and R.H. Friend and by H. Chayet, V. Savvateeyv, D. Davidov and R. Neumann. Chapters by S. Tasch, W. Graupner, and G. Leising and by Y. Z. Wang, D. Gebler, and A. J. Epstein describe OLEDs based on poly(paraphenylene) and poly(pyridine), respectively. The book concludes with a chapter on polyfluorene-based devices, which show great promise for producing light in all colors from blue to red.